The present invention relates generally to the reduction of emissions produced by lean burn engines. In particular, the present invention provides improved systems and methods for reducing oxides of nitrogen (NOx) emissions from existing in-use diesel engines.
According to EPA, on-highway trucks account for 10% of all NOx emissions and over 30% of the on-highway NOx emissions. Selective Catalytic Reduction (SCR) can reduce NOx emissions by 60-85% over the EPA heavy duty Transient Emissions Test. SCR technology is considered to be a leading technology to help truck engines meet the stringent 2007 model year NOx emission standards.
An example of prior art SCR technology is disclosed in U.S. Pat. No. 5,924,280 to Tarabulski entitled “Reducing NOx Emissions from an Engine While Maximizing Fuel Economy” which is incorporated herein and made a part hereof by reference. U.S. Pat. No. 5,924,280 employs SCR and EGR technology in combination over various engine load operating ranges.
The NOx mass flow from in-use diesel engines varies based on the year of manufacture, horsepower, options/features for driver convenience, fuel economy benefit and/or to meet legislated emissions limits. The use of selective catalytic reduction requires the injection of a reagent proportional to the mass flow of the NOx output from the diesel engine. For engines with or without SCR systems, NOx output is estimated in some manner, as there is no feedback system available that has the response time to reliably, economically and continuously determine NOx mass flow on a commercial vehicle.
It is necessary for engine manufacturers to assure NOx mass flow is below legislated limits for new and in-use engines. Further, to retrofit an SCR system, the process of determining NOx mass flow needs to be revisited for each engine type, horsepower rating, and engine map.
There are numerous state or local government incentives being created to encourage equipment owners to apply retrofit technology.
It would be advantageous to provide a cost-effective solution for retrofitting existing mobile diesel truck fleets with SCR technology. It would also be advantageous to retrofit equipment with an SCR system without extensive downtime, engine removal, dynamometer tests, or road trips to test facilities. It would be further advantageous to provide methods and systems for customizing SCR systems for retrofitting on various types and models of diesel trucks, based on an initial testing period to determine NOx emissions under various conditions. It would be further advantageous to use a reagent in the SCR system.
The methods and systems of the present invention provide the foregoing and other advantages.